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2013-2014 Soil Survey Update for Rhode Island

A new version (published December 18, 2013) of the RI Soil Survey maps and data is now available for download from the Web Soil Survey (source for official USDA-NRCS Soil Data, a RIGIS copy will be available soon). This new soils version contains numerous improvements, update soil mapping for the entire RI coastal zone (dunes, marshes, and beaches), error fixes, and adjustments to the hydrology along major rivers and streams. Aiding in the update mapping is the use of recently released state-wide Lidar elevation data and derived products such as 2 foot elevation contours, wetness index, and slope maps. RI soils data is currently being improved by yearly updates to the data. The following provides additional information about the changes found on the 2013 version. Please download this new version for use on your GIS.

Phase III of the RI Coastal Zone Soil Survey:

The 2013 soils data contains a complete re-digitization and classification of the soils for the entire RI Shoreline as part of the on-going Coastal Zone Soil Survey of RI (this fixes the "spatial shift" so beaches are accurately mapped). Beaches are now mapped and classified based on their dominate surface fragment size: Map unit Ba is dominated by sand and gravel surfaces, Baz is dominated by cobble to stone size surfaces, and Bax is mostly boulder (> 24 inches) size surfaces. Several new coastal ponds and coves in Narragansett Bay are also included (such as Long Pond in Little Compton and Bissell Cove in North Kingstown) and the dunes and marshes along Narragansett Bay have also been re-digitized and classified to the series level. A fourth phase of the coastal zone soil survey is currently on-going and planned for release next year (2015). See comparison of 2012 (yellow polygons) to 2013 (red polygons) soils below - note the complete mapping of beaches and adjustments of water bodies.

Coastal Soil Comparison

 

 Reshaping of the major rivers and hydrology:

When the original soils data was digitized in the 1990’s the only available base map for use was USGS Topo Quads, as a result there is a “spatial shift” in the soils data when it is overlaid on modern orthophotography causing the soil map units to not align with the imagery perfectly. An effort has been underway to correct this error, for example Block Island was re-digitized last year to correct the shift (see 2012 update page). This 2013 soils version has re-digitized all of the major rivers and streams so they now match the orthophotography (see example below), the associated riparian areas and hydric soils (wetlands) along the flood plains were also adjusted to match the hydrography and elevation contours.

Adjustments to rivers in soil update

 

 Use of Lidar for adjusting hydric soil map units:

In 2011 Rhode Island acquired a 1 meter resolution State-wide LiDAR elevation data set which was used to derive products that are extremely useful for modern day soils mapping. A state-wide set of 2 foot contours, wetness index (maps showing concave slopes where water is moving into), slopes, and curvature maps was produced and used for updating areas where the hydric soil (Rf map unit mainly) boundaries were incorrect due to the spatial shift (this was mainly done for Providence County). The lidar was also used to adjust the organic soils (swamps and bogs) in many areas of the state. Below is an example of the comparison of the previous (yellow polygons) and the updated 2013 soils (red polygons).

Comparison of hydric soil units

Below is the area of detail from image above - note the 2 foot LiDAR elevation contours and the Rf (hydric soils on drainage ways) map unit; the 2012 soils data has the Rf unit going over the hilltop (convex slope), the new 2013 soils shows it in the concave drainage swale resulting in more accurate hydric soil delineations for wetland protection.

Comparison of Rf soil map units

Future Updates:

The National Cooperative Soil Survey is undergoing restructuring to a more regional organization and the future focus for the NCSS is not in improving the accuracy of the spatial mapping but rather refining the tabular data (Soil Data/Join and recorrelation as it is called). The RI NRCS and the RI soil staff is trying to continue to improve the spatial (and tabular) soils data by continuing yearly updates to improve the location of the soil boundaries.

For more information on the RI Soil Survey Program contact Jim Turenne at 401-822-8830 or jim.turenne@ri.usda.gov